1. Field of the Invention
The present invention relates to a simplified planetarium apparatus which is able to project a starry sky simply in a home environment, and an image projecting apparatus which is capable of projecting images.
2. Description of the Related Art
A planetarium apparatus which reproduces the starry sky and moves the starry sky as desired artificially even in the daytime achieves not only reproduction of the beautiful starry sky day and night for appreciation, but also reproduction of a celestial motion such as stars (fixed stars). Therefore, it is used all over the world as a preferable apparatus for leaning astronomy.
FIG. 9 illustrates a basic configuration of a known optical planetarium apparatus. A stellar projection sphere 48 is supported so as to be capable of rotating about a diurnal axis 44, and the angle is set to an angle 46 which is the same as the latitude of an observation point. Reference numeral 43 designates a light source, which is set to the center of the stellar projection sphere 48. A plurality of projection units 52 are arranged on the surface of the stellar projection sphere 48 at predetermined angles. Light emitted from the light source 43 passes through condenser lenses 51, stellar base plates 50 having through holes corresponding to stars on a light-shielding material, and projection lenses 49 of the projection units 52 and focuses on a dome screen 47 to reproduce an image of the starry sky. Since the range of reproduction by the single projection unit 52 is limited, the plurality of projection units 52, for example, twelve to thirty-two projection units 52 are arranged to cover the entire sky, so that an artificial starry sky which is similar to the real starry sky is reproduced.
Assuming that the center of the stellar projection sphere is a view point, the apparatus shown in FIG. 9 is able to project the stars at quite accurate positions on the dome screen. In addition, through the usage of the lenses, a sharp and realistic starry sky is reproduced. Examples of the optical planetarium apparatus being similar in basic configuration are described in Japanese Patent No. 2632438 and Japanese Unexamined Patent Application Publication No. 43781/1986.
FIG. 10 illustrates a basic configuration of a known pin-hole type planetarium apparatus. Although the basic configuration is similar to the optical planetarium apparatus, through holes 42 which correspond to the stars are directly formed on a light-shielding stellar projection sphere, and the light source 43 is installed therein. The light emitted from the light source 43 passes through these through holes 42, and is projected onto the dome screen 47, which has a look of the starry sky. The stars are projected at the accurate positions in the same manner as the optical planetarium apparatus. In Japanese Unexamined Utility Model Registration Application Publication No. 144341/1980, an example which is similar to the pin-hole type planetarium apparatus in basic configuration is disclosed.
The optical planetarium apparatus in the related art as shown above has a configuration in which the plurality of projection lenses and the stellar base plates are used, and these members are assembled to the stellar projection sphere. Therefore, there are problems such that the structure is complex, a large number of components are necessary, the part production cost and the assembly and adjustment cost are high, and the weight of the apparatus body is liable to be heavy, so that the handling is difficult. Therefore, the usage is limited to places such as public facilities having sufficient financial resources. In contrast, since the pin-hole type planetarium apparatus does not use lenses, the configuration is significantly simple in comparison with the optical planetarium apparatus. However, since it has a configuration to project shadows, it is difficult to obtain sharp images. In order to obtain the sharp images, it is necessary to use a light source having an extremely small light-emitting point, so that the choice of the light source is limited.
Furthermore, since the stellar projection sphere is composed of a polyhedron formed by assembling spherical materials or flat materials, punching holes on the spherical surface is costly, and when assembling flat projection base plates, there arise problems of operating cost and generation of joints. In addition, since the projection base plates are exposed directly to the outside air, the star image is subjected to the influence of dust.
The planetarium apparatus is a superior apparatus in which the sky with full of stars as great outdoors is reproduced, and enjoying such starry sky not only in the facilities but also in the home environment, or studying the movement of constellation is in demand in the world. However, in order to satisfy such demand, it is desired to be able to project the stars directly in the room in a rectangular parallelepiped shape without the dome screen since installation of the dome screen is difficult and complicated. When the above-described optical planetarium apparatus and the pin-hole type planetarium apparatus are used in the home environment, the stars and constellation can barely be projected on a flat plane in a recognizable image quality. However, when the image is overlapped with the corners of the room or with the furniture, the positions where the stars appear are significantly distorted, and hence the constellations cannot be recognized easily. Depending on the colors of the furniture, the image itself cannot give good definition. When the optical planetarium apparatus is carried in, the projection lenses by themselves move and the distance with respect to the wall surface which serves the projection screen varies in complex manner, so that the image may go out of focus, and hence the distance of the space between the lenses varies, whereby the shape of the constellation may be distorted.
From these reasons, it is difficult to serve the needs of enjoying the beautiful starry sky and learning the constellations at home with a low cost apparatus.